For IC (integrated circuit) designers, the ideal semiconductor memory includes random accessibility, non-volatile characteristics, increased capacity, increased speed, reduced power consumption, and unlimited reading and writing functions. Resistive random access memory (RRAM) technology has been gradually recognized as having exhibited the aforementioned semiconductor memory advantages.
Please refer to FIG. 1, a conventional single-pole operation resistive random access memory 10 with a single oxide layer is shown. The resistive random access memory 10 includes a Pt bottom electrode 14, a dielectric layer 16 of nickel oxide, and a Pt top electrode 18 sequentially formed on a substrate 12. The structure of the conventional resistive random access memory 10 can be represented as below: Pt/NiO/Pt. The conventional resistive random access memory 10, however, exhibits extremely unstable operating voltage (in particular SET voltage) after repeated and continuous conversion of resistance, resulting in loss of endurance.
U.S. Pat. Publication No. 20070215977 discloses a resistive random access memory 20 with two adjacent oxide layers, as shown in FIG. 2. The resistive random access memory 20 includes a lower electrode 22, a first oxide layer 23, a second oxide layer 24 doped with transition metals (serving as current control layer), and an upper electrode 25 sequentially formed on a substrate 21. In comparison with the conventional single-pole operation resistive random access memory 10, the resistive random access memory 20 has lower on-current. Even so, the resistive random access memory 20 does not improve upon endurance.
Therefore, it is necessary to develop a resistive random access memory with superior endurance and reduced on-current.